A method for treating osteoporosis in a subject in need of such treatment includes administering orally to the subject an effective amount of an extract product of a Dioscorea species capable of promoting proliferation and differentiation of bone marrow cells in the subject. Particularly, the Dioscorea species is Dioscorea alata L. cv. Phyto, characterized by a randomly amplified polymorphic DNA (RAPD) fingerprint including 14 DNA bands ranging from 428 bp, 452 bp, 537 bp, 602 bp, 723 bp, 817 bp, 934 bp, 1140 bp, 1242 bp, 1478 bp, 1641 bp, 1904 bp, 2151 bp and 2918 bp, respectively, when genomic DNA of the Dioscorea species is amplified with a primer of SEQ ID NO:9, and the extract product is prepared by a process including: (a) extracting a tuber of the Dioscorea species using an alcohol-based solvent in the presence of acetic acid; (b) subjecting the resultant product obtained in (a) to a separating treatment to obtain a soluble fraction; and (c) removing solvent from the soluble fraction obtained in (b) to extract fractions of Dioscorea sp.